To use this system, aspell-autobuildhash expects a $lang.compat file in /var/lib/aspell ($lang stands for the lang basename with variant if any, e.g. $lang is something like gl-minimos or en)) containing aspell compatibility version for last successful build or ``0'' or en empty file if hash is to be rebuild, as is for dictionary installation and upgrades.
When upgrading aspell, script will check if version in $lang.compat is different from aspell.compat and rebuild if so, updating $lang.compat with the new value.
Wordlists should previously be compressed either with gzip (and their extensions set as .mwl.gz or .wl.gz) or preferably first with aspell prezip and then gzipped (with .cwl.gz extension). This applies both for plain wordlists and munched wordlists (in the ispell way) if you use affix compression.
If your package will provide a single hash, install prezipped+gzipped wordlist as /usr/share/aspell/$lang.cwl.gz or, if prezip is not used, as /usr/share/aspell/$lang.mwl.gz.
If your package will provide more than one aspell hash for the same $lang, you will need to place each compressed wordlist as e.g. /usr/share/aspell/$subdict.cwl.gz, and the common $lang.compat as above. Then create a /usr/share/aspell/$lang.contents file with the base names of the subdicts, one in a line. For English that will contain, amongst other possible lines
en-common en-variant_0 en-variant_1 en-variant_2 en_CA-w_accents-only
No need to use this file if a single hash is being created.
Dictionaries-common scripts will call internally this script and create a single hash file at /var/lib/ispell/$lang.rws, or hash files at /var/lib/ispell/$subdict.rws. You must set a symlink to that files from /usr/lib/aspell/$lang.rws or /usr/lib/aspell/$subdict.rws as appropriate.
Aspell dictionary packages using this script must make sure that $lang.compat is reset on every new install/upgrade, so hash is rebuilt. They must also make sure that $lang.compat and all of /var/lib/aspell/$lang.rws or /var/lib/aspell/$subdict.rws are removed on package removal.
As of version 1.10, installdeb-aspell script will understand 'auto-compat' and 'auto-contents' fields in $dict.info-aspell file to help with this by adding needed debhelper snippets. Put in that entry the base name(s) of your compat and contents file(s) and carefully check resulting maintainer scripts after build.
Note that you are no longer suggested to ship empty files at any of /var/lib/aspell/$lang.compat, /var/lib/aspell/$lang.rws or /var/lib/aspell/$subdict.rws, but explicitly create/update them on install and explicitly remove them on removal.
aspell maintainer should also call this script from package postinst. When comparing versions it will get the aspell version from file /usr/share/aspell/aspell.compat.